Transmission Controls With PCM

Diagnostic Chart:

Wiring Diagram:

SELECTOR SWITCH - UNDEFINED DATA
The PCM determines which gear is selected by a combination of opens and grounds in circuits 771, 772, and 773 at the selector switch. Each combination indicates a specific selection on the manual shift quadrant (P, R, N, D, 3, or 2). Circuit 776 is either open or grounded to produce an even parity for each manual shift quadrant. Undefined data indicates that at least one of the circuits 771, 772, or 773 was open when it should have been grounded or was grounded when it should have been open.

DTC PARAMETERS
DTC 46 is set when the PCM has detected the following conditions twice per ignition cycle.
^ An undefined bit pattern, of all circuits 771, 772, 773, and 776 grounded for greater than 500 milliseconds.
^ An undefined bit pattern for greater than 3.5 seconds.
^ Selector switch diagnostic trouble codes will result in 2nd gear starts.

On 1991 Perf (LLO), and all 1992, 1993, and 1994 vehicles, the difference between DTC 46 and DTC 49 is that a possible bit pattern error due to misadjustment cannot set a DTC 46.

TEST DESCRIPTION
Numbered steps below refer to steps on trouble chart.
1. This step verifies the conditions for DTC 46 still exist.
2. For 1992,1993 and 1994 vehicles, DTC 46 is separated into two codes. DTC 46 is set by an invalid data condition which will not set due to a misadjusted shift cable. DTC 49 diagnosis an invalid data condition which may be caused by cable or a switch misadjusted.
3. A ground indication in a particular gear would be caused by two circuits being grounded while the switch is grounding two others.
4. The PCM/TC supplies 12 volts to each selector switch circuit. This step tests for that voltage.

DIAGNOSTIC AIDS

* Select MALF History from Scan tool Transmission Control Module (TCM) menu.

Check the tightness of the female terminal grip with a spare male terminal.

When the PCM detects a fault in the circuit (open, ground, short) the PCM will open the circuit internally to protect the circuit.
^ On 1991 vehicles if no circuit problems can be detected, check shift cable and selector switch for proper adjustment.
^ On 1992, 1993 or 1994 vehicles a DTC 46 cannot be set due to misadjustment.
^ This DTC will cause the transaxle to start out in 2nd gear.